A film cassette with a spool lock for preventing unintended rotation of the film spool and a light shield for preventing ambient light from entering the cassette interior is known in the prior art. U.S. Pat. No. 5,115,268 issued May 19, 1992 discloses a film cassette comprising a light-trapping plush for preventing ambient light from entering the cassette interior through a film egress/ingress passageway, a film spool supported for rotation in film unwinding and film winding directions, and a locking pawl supported for movement into engagement with the spool to secure the spool and out of engagement with the spool to release the spool. The spool has a coaxial ratchet wheel with asymmetrically shaped teeth. The locking pawl appears to be a rigid beam member which is pivotally mounted at one end and has an asymmetrically shaped detent portion at an opposite end. A curved spring arm portion of the locking pawl extends from the end of the rigid beam member that has the detent portion, to bias the detent portion to between any two adjacent ones of the teeth in order to secure the spool. To remove the detent portion from between the two adjacent teeth, an engagement release portion of the locking pawl is turned to pivot the rigid beam member against the contrary urging of the spring arm portion. The engagement release portion then is held in the turned-to position to maintain the detent portion separated from the ratchet wheel. When the engagement release portion is released, the spring arm portion is free to pivot the rigid beam member to return the detent portion to between any two adjacent ones of the teeth in order to re-secure the spool. Since the teeth and the detent portion are asymmetrically shaped, it appears that the locking pawl can be temporarily forced out of engagement with the spool against the contrary urging of the spring arm portion when the spool is rotated in a winding direction.